Sound reproducing apparatus



Jan. 17, 1939. R. H. DRElsBA'cH .2,144,566

' souNn REPRoDUcmG APPARATUS A Filed Feb. 5, 1958 IN V EN TOR.

Rom/11H6 BY Q @y umm mmnl- ...,Humml ,f W" Talen/EY.

Patented Jan. `17, `1939 PATENT orio Y SOUND RPRODUCING APPARATUS Robert H. Dreisbach, Fort Wayne, Ind., assigner,

by mesne assignments, to The Magnavox Coinpany, Incorporated, Fort Wayne, Ind., a corpo- K' ration of Indiana l y Application February 5, 1938, SerialNo. 188,894

rciaims. (ci. 17g-'1004) is associated with the apparatus to improve the The presentl invention 'relates to sound reproducing apparatus, and more particularly to phonographs of the type that employ an 'electrical pick-up onthe record and an electrodynamic sound reproducer for propagating the sound program.

An object of the invention is to provide a new and novel mounting for the sensitive sound reproducing elements of an electrical phonograph of the type using an electrodynamic loudspeaker, in which said sensitive apparatus is supported in a free floating manner so that vibrations produced in the cabinet by the sound reproducer will not be transmitted to said sensitive apparatus.

Another object of the invention .is toprovide a new and novel mounting for an electrical phonograph of they character. described, in which the sound record-supporting platen, its associated pick-up and the record platen driving motor `are all supportihgasa unitary. structure in a free floating manner in a` cabinet.

Another object of the invention is to provide a new and novel support for a sound 'record supporting platen, its driving motor and asso-V ciated tone arm in a vfree oating position within a cabinet and in which an inertia supplying mass is provided upon the support to render the apparatus substantially static with! respect to vibrations of the cabinet..

. Another objectV of the invention is to 'v provide a newand novel spring mounting for supporting a record carrying platen and an associated tone arm of an electrical phonograph in a cabinet, inV which the spring mounting. can be rendered temporarily inoperative to firmly secure said apparatus upon the cabinet for transportation.

Other objects and ad-vantages o-f the invention will be in part pointed out `and in part evident to those skilled in the art, fromv the following description taken in connection with the accompanying drawing', wherein there vis shown by way of illustration and not `of limitation preferred embodiments thereof. t f In the drawing,-

Figure 1 is a vertical sectional View of a sound reproducing phonograph Vof the type employing two electrodynamic loudspeakers,y

, Figure 2 is a fragmentary detailed view, in section, showing a preferred form of resilient mounting means constructed andr arranged inraccordance with the present` invention, Y. v y

Figure 3 is a modied form of the invention in "which ,thi-weight, of a therriliceiftubegampler operation of the resilient supporting means, and

Figure 4 is a View of the underside of the motor board of a phonograph showing a preferred form for an inertia mass supplying weight, as

contemplated by the invention.

In the reproduction of sound from a record by electrical means of the character described, 'in which a modulated electric current is generated .by a-pick-up engagingv a moving record, it is important that the pick-up needle follow the sound track and be free of any other extraneous force, such as vibrations which, as is well known, set up a false signal. One of the difficult problems with apparatus of this character is in providing a means that will prevent mechanical vibrations such as are produced by the phonograph driving motor and other associated apparatus from being transmitted to the sound record and pick-up device. A,

In the past others have provided various forms of shock absorbing resilient supports for the tone arms and driving motors of record supporting plat'ens, which operate to absorb vibrations that might be transmitted between these, elements. However, upon the adoption of electrodynamic sound reproducers in connection vwith phonographs of this character, therehas `been introduced a new problem, which in many rel spects is more diflicult to overcome, for the reason that such a sound reproducer, when mounted upon or within a cabinet, setsup Vibrationsof considerable magnitude in the cabinet, which vibrations cannot be eliminated by the arrangements and expedients taught by theprior art.k

an electrical phonograph of the type employing one or more electrodynamic sound reproducers Y mounted in the same cabinet, the present in- 35 To overcome the above problem and provide an additional weight or static inertia supplying mass which will react and cooperate with theA resilient supporting means to effectv an absorplpick-up device I2.

tion of substantially all vibrations of the cabinet, and thus render the sound record and pickup needle relatively immovable, except for that relative movement which is caused by the rotation of the record and the particular movements imparted thereto by the soundtrack upon the record.

In Figure 1 of the drawing the invention is shown as embodied in a phonograph of the'type employing a tall cabinet I0, in the lower portion of which there is mounted two electrodynamic sound reproducing devices II that propagate as sound waves the signals generated by a Located in the upper part of the cabinet I0 there is a sound record I3 with which the pick-up device I2 cooperates. The pick-up device I2 is mounted upon a swingable tone arm I4 that is pivotally secured upon a pedestal I5, and the record is shown as carried by a horizontally disposed record supporting platen I6 which is adapted to be driven by a motor I'I. The pick-up I2 is shown as connected through a suitable cable to a terminal board I8, and extending downwardly from the terminal board I8 there is an additional cable I9 that serves to conduct the sound signal currents generated by the pick-up I2 to an amplier 23 which functions, as is well understood-to amplify Ythe signal currents and provide excitation for the electrodynamic sound reproducers II by means of conductors 2| and 22. Extending-from Ythe terminal board I8 there is also a lead 23 having a connector 25 Aat the end thereof, by means of which the phonograph may be connected to any suitable service outlet. The motor .II is connected to the terminal board I8 by'm'eans of a-cable 26, and it is adapted to be controlled by a suitable control unit 2'I, which is likewise connected to the terminal board I8 by means of a cable, as shown. The control unit 21, in addition to controlling the motor I7, also provides a means whereby the tone and volume of the'sound reproducersI I may be varied. Knobs 28 and 29'are associated with the control unit 21 for this 4purpose.

In practice-'it is customary to mount the sound reproducing ldevices II in a baffle Y3E! at the front' of the cabinet, and in front of thisbaiie there is usually disposed an open grill-work or other form of ornamentation 3I through qwhich the propagatedY sound is projected. With this arrangement, and particularly where the sound Ysignals reproduced are in the low frequency range, the electrodynamic sound reproducers II set up a definite vibration in the cabinet walls. This'vibration is partly due to the mechanical'connection of the reproducers with the cabinet, and also because of the compressional Wave vibrations set up within the cabinet at the back of the reproducers, which ,are often greatly accentuated by the resonance of the cabinet itself. Toprevent transmission of these vibrations, which are set up in the cabinet IIJ by the sound reproducing device I I, the present invention contemplates a mounting of the pedestal I5 together with the pick-up I2 and its tone arm I4, and the sound record supporting platen I6 and its driving motor I'I upon a `resiliently mounted vsupporting member 32, so that these elements will beheld in a relatively xed operative relation with each other, and in a free'oating manner with respect to the cabinet. e

In vFigure 2 of the drawing there is shown a preferred form of resilient mounting for the supporting Vmember '32. As hereshown, `the cabinet I0 is preferably pro-vided with a rectangular shelf-like projection 33 which extends around the inner walls of the cabinet at the upper part thereof.- However, thisshelf-like projection 33 might be provided by shelf-like members upon opposite walls of the cabinet.

In the preferred arrangement the supporting member 32 is in the formrof a rectangular motor board or panel upon which the record carrying platen I6 and the pick-up vI2 are mounted, and below which the platen driving motor II is mounted in suspended relation. With such a supporting member 32 there is preferably provided at its four corners a downwardly extending stud 34 which passes freely through an opening 35 in the shelf-'like member 33. As here illustrated, the shelf-like member 33 is provided with-countersunk portions 36 and 31 which extend respectively into the top and bottom sides of the shelf-like member 33 concentric with the opening .135. Disposed within these countersunk portions 3B and 3'I of the opening 35 there are respectively conically wound' spiral springs. y38 and 39 which surround the stud 34. The spring 38 .is adapted at` its upper end to engage anenlarged head 40 upon the stud 34 andthus yieldingly hold this stud .against downward displacement,.and the spring 39is adapted at .its 'lower end to engage a securing means :or Vnut 4I carried by the stud 34 to yieldingly resist .any up- 'ward movement of the stud Y34'. YIn addition to 4I] of the'stud 34 may be drilled and .threaded to receive a screw 42' for .securing the supp-orting member .32 thereupon. At this ypoint it vwill be noted that with such .an .arrangement the resilient supports may be fully assembled beforethe supporting member 32 and its associated apparatus `is placed in the cabinet I0. .By properly designing the springs 38 and 39 with respect to resilience and the totalmass carried by the support 32, and also adjusting 'the compression of the springs '38 and 39, it is possible with this arrangement to provide a resilient mounting for the more sensitive elements of the phonograph which will preventthe transmission. of any .vibrations from-the cabinet 4to these elements. .To thisend the .present invention .also contemplates a proportioning of the -total mass of the resilient supporting apparatus, and the distribution of this Ymass with respect to the several resilient supporting means, so that such means will-function uniformly, and thus insure a free-floating of the more sensitive elements with respect to the cabinet. This is accomplishedV by securing a weight 43, as shown in Figure 1, preferably to the underside of the supporting member 32, as will be more particularly pointed out hereinafter.

As an additional feature of the present invention, this figure of the drawing also shows a bracket 44 having a central opening -45, which is adapted to be placed over the extending end of the stud 34 where a wing nut r4I may lbe threaded upon theend of the stud 34. The purpose of this bracket -44 is toprovide a convenient means for securing the resilient 4sup-l in transit, and when in use with the nut 46 securely tightenedl upon thesstud 34, the supporting member 32 will be drawn down firmly against the upper surface 41 of the shelf-like member V33, where the springs 38 and 39 will be rendered inoperative and-.protected against damage :due to shock when the phonograph is in transit.

In Figure 3 of the drawing there is shown a modication of .the present invention, wherein the weightV lof the more sensitiveelements of the phonograph carried by the supporting member 32 is supplemented by the weight of a thermionic tube amplifier 48. When this expedient is resorted to, theweight 43 may be dispensedwith. For the purposeof providing a distribution of this mass upon the supporting member 32, it will be understood that the positionv of the amplier 48, with respect to the center of gravity of the entire mass, will be so positioned as to equalize the weight between the several resilient supporting means upon which the supporting member 32 is mounted. As shown, the 'ampliiier 48 is suspended from the underside of the supporting member 32 by means of abrack'et 49, but it will be understood that the amplifier 48 may be secured to the supporting member 32 in any other suitable manner.

In Figure 4 of the drawing there is illustrated the underside of a motor board o r supporting member 50 having a static inertia mass supplying weight 5| secured upon the underside thereof. The motor board 50 in this instance is of elongated congurationand has a record driving motorv 52 secured at one side of its center. A Ytone arm supporting pedestal, designatedy by the numeral 53, is mounted upon the upper side of the supporting member 50 vover an opening 54 at one corner thereof through which pick-up conductors 55 extend. Because of the disposition of the record driving motor 52 at one side'of the center of the motor board 50, and also because of the aperture 54 therein, the weight 5I is rounded out at one corner, as at 56, and at this end the weight 5| is also increased in cross-section, as at 51. This increase in cross-section of the weight 5| is to compensate for the off-center disposition of the motor 52 and the other apparatus upon the motor board, and thus provides a motor board having a uniformly distributed total weight between the four corners thereof.

While I have, for the sake of clearness and in order to disclose my invention so that the same can be readily understood, described and illustrated specific devices and arrangements, I desire to have it understood that this` invention is not limited to thespecic means disclosed, but may be embodied in other ways that will suggest themselves to persons skilled in the art. It is believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims. are to be considered as part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In a sound reproducing phonograph, the combination of a cabinet, a sound reproducing device of the electrodynamic type mounted upon said cabinet, a sound record supporting platen having a driving motor, a tone arm having an electrical pick-up device adapted to swing over a record upon said platen and provide an exciting current for said electrodynamic sound reproducing device, a free oating support for said record supporting platen, its driving motor and said tone arm, said free iioating support being mountsaid cabinet, a sound record supporting 'platenl having a driving motor, a tone arm having an electrical pick-up device adapted to swing over a record Vuponsaid platen and provide an exciting current for said electrodynamic sound reproducing device, a free floating horizontally disposed panel upon which said record supporting platen, its driving motorv and said tone arm .are

lmounted, said panel being supported by shock absorbing means disposed between it and said cabinet, and means providing a stabilizing inertia supplying mass iixedly attached to said panel, the mass of said means being distributed substantially uniformly between said shock absorbing means and being of sufficient weight tol cause said shock absorbing means to absorb all vibrations transmitted thereto by the cabinet.

3. In 'a sound reproducing phonograph, the combination of a cabinet, a sound reproducing device of the electrodynamic type mounted upon said cabinet, a soundy record supporting platen having a driving motor, a tone arm having an electrical pick-up device adapted to swing over a record upon said platen and provide an exciting current for saidelectrodynamic sound reproducing device, Ya free floating horizontally..v disposed panel upon which said record supporting platen, its driving motor and said tone arm are mounted, said panel being supported at its corners upon spring means carried by said cabinet, and an open frame-like weight attached to the underside of said panel, said frame-like weight being adapted to extend in a rectangular path closely adjacent the sides and ends of said panel to distribute its weight substantially uniformly between the four corners of the panel and being" of. suiiicient total weight to cause said spring means to absorb all vibrations transmitted thereto by said cabinet.

4. In a sound reproducing phonograph of the character described, the combination of a cabinet, a pair of spaced horizontally disposed shelf-like supports extending inwardly from opposite walls of said cabinet, a motor board disposed in overlapping relation with said shelf-like supports, said supports having openings therethrough at points corresponding to the corners vof sai-d motor board, a securing stud extending from each corner ofl said motor board through said openings and having a securing means at the other side of said shelf-like supports, and a spring means disposed about each of said studs between said shelf-like ofjsaid cabinet, :a `motor board for :mounting phonographic apparatus disposed in .overlapping relation with said shelf-like supports, said supports having openings therethrough at points corresponding to the .corners of said motor board, a

securing means extending from each corner of Vsaid motor board through said openings and .hav- Y ing a threaded means at the outer ends thereof, a springmeans disposed about each of said securing means between said .shelf-likeY supports andsaid .motor boardand between saidthreaded means yat .the ends Aof said securing means .and-saidshelf-v like members, said spring means being arranged in opposed relation upon VsaidA securing means and adapted to support said motor board'inV a -oating position free of said shelf-like supports,

and a static :inertia supplying mass vcarried by said motor board supplementing theweight of the apparatus thereupon ,and cooperating with said spring means to prevent the transmission of Vibrations from the lcabinet to said motor board.

6. In a vibration absorbingY support for sensitive .sound reproducing apparatus, the combination of a cabinet having-a xedinwardly extending .shelf-like member With an opening therethrough, an apparatus supporting member disposed within said cabinet in overlapping relation With said shelf-like member, a resilient shock absorbing means dispos-ed between said Vshelfli-ke member and said apparatus supporting member, a stud upon said apparatus supporting member extending freelythrough the opening in said shelf-like member, la threaded securing means at the outer end of said stud, and a second resilient shook absorbing means disposed between the other side of `said shelf-like member and said threaded securing means `cooperating with `said first resilient :shock absorbingmeans to1provide aviireeY oating .support for said apparatus "supporting ymember,tlflefseeuring means at the outer end Osaid-Stud being adjustable to vary the degree of compression ,of said :two resilient shock absorbing means,nwhereby the resilience thereof may be adjusted to vary the shock `absorbing characteristics thereof.

'7. In a vibration Aabsorbing support for sensiltive Lsound reproducing apparatus, the combination of a Ycabi-net having a xed shelf-like membier Withanopening therethrough, an apparatus supportingsmember kdisposed Within -said cabinet in overlapping relation With said shelf-like mem- V ber, a resilient shock -absorbing'means disposed between said shelf-like member and said apparatus supporting member, a'securingmeans for said rapparatus supporting member extending freely through the opening in said shelf-like member, a threaded means at the end of said securing means, and aisecond resilient shock absorbing means disposed between the other side of said shelf-like member and vsaid threaded means and cooperating With said first resilient rshock -absorbing means toprovide-a `free "floating support for :said apparatus supporting member, said securing means being extended out beyond said threaded means, anda-clamping member having a central opening adapted to be positioned over the lend of saidsecuring means and tightened thereupon by a secondrthreaded means to compress said first resilient shock absorbing means and firmly secure said apparatus supporting member Aagainst said shelf-like member as when thecabinet is Jin transit.

ROBERT H. DREISBACH. 

